The present invention is generally directed to a filter through which lime passes during its transport from a source to a processing pot in a steel mill where it is used to purify steel during processing. The present invention is particularly directed to an improved filter having a plurality of openings to selectively permit lime to pass through, while retaining contaminants that are larger than the lime particles. The present invention is more particularly directed to reinforcement of the perimeter of the openings, said reinforcement directed to reducing degradation of the filter by the lime.
Powdered or granular lime is transported from a location where it is obtained to a steel mill wherein it is employed to purify steel processing. Lime is also used to coat the processing pot and other receptacles where steel is being melted to prevent steel contacting steel. For about the past 22 years, the method of transferring lime to a steel mill was to deliver it by means of a railroad car to a location close enough to a steel mill so that the lime could be transferred from the railroad car to the steel mill by means of a tubing. Generally, the lime was released from the bottom of a railroad car into a receptacle under the box car, said receptacle terminating in a tubing located below ground. A blower connected to the tubing produced air or other gas which urged the lime through the tubing to a day tank with about 2,000 ton capacity, from which nitrogen gas urged the lime from the day tank through a tube connecting the tank and receiving tank in a steel mill. The lime was conveyed from the receiving tank to a processing pot by a rear gear or auger screw.
One problem with this method is that lime settled in the receptacle under the railroad car, got wet, compacted, solidified, combusted or entered other undesirable states or dangerous states. Moreover, below ground tubing was difficult to repair.
A more serious and expensive limitation of this conventional method is caused by contaminants in the lime. Contaminants in lime generally include bricks, bottles, rocks, plastic dishware and the like. Contaminants enter the lime as it is being removed from its source and is transported to a steel mill. If they reach the steel mill, they impair or destroy the rear gear. Such a gear costs approximately $65,000. In addition to being very expensive, replacement of the gear also may be difficult or time consuming. Using conventional lime transfer methods, the gear had to be replaced at the rate of about one per month, a costly loss. An even more serious repercussion of contaminants destroying the gear is that before the gear is recognized as needing replacement, its malfunction can lead to explosions and damage costing at least $500,000.
An improvement on the railroad car-underground tube lime-transfer method is to use a pneumatic tank truck (trailer) for transport of the lime. In this method, a tube is connected directly to the truck, and the lime containing truck is pressurized to transfer lime from the truck to a day tank. Transfer from the truck to the day tank is generally by means of tubing connecting on a first end to a fitting on the truck tank and on a second end to a first end of a coupling apparatus. The second end of the coupling apparatus is joined to a tubing leading to the day tank. From the day tank, the lime was transferred to the steel mill through tubing in a conventional manner, that is, by tubing connecting the day tank to the steel mill, the lime being urged to the steel mill by means of nitrogen gas pressure pumped into the day tank.
The truck transport method solved some problems, for example, the need for underground tubing and the risk of wetting the lime. However, damage to or destruction of the rear gear in the steel mill by contaminants in the lime occurred at the same rate as in the conventional method, so the most serious problem remained.
Accordingly, there is a need in the art for a method to transfer lime to a steel mill which minimizes the risk of damage to the receiving structures of the steel mill by contaminants in the lime such as bricks, bottles and disposable dishes. There is further need in the art for a filter to remove the contaminants from the lime which is simple yet effective. There is a still further need in the art for a filter which lasts a relatively long period of time, that is, is not readily degraded by lime.